Dropping www won’t display index.php

I recently upgraded from WordPress 2.6.1 to 2.7.1. Now when I try to access https://www.gamebits.net/ in Firefox 2.0.0.20, I get this error message:

https://www.gamebits.net/screens/72d1748c0543434689b374545d13d4b3.jpg

If I tell Firefox to open the file itself, I get a blank page loaded from file:///Users/kgagne/Desktop/f1w39dmj-1 which proves to be a local copy of index.php.

This does not happen in Safari 3.2.1 when I access https://www.gamebits.net, but if I drop the www and go just to gamebits.net, the page won’t load; instead I end up with a file on my desktop called gamebits.net that is identical in content to WordPress’s index.php file.

Any idea what could be causing this?

-Ken